Regarding a work machine, in order to make it possible for arranging in a limited space without occupying a large space, and to provide a hydraulic fluid energy recovery apparatus and a hydraulic fluid energy recovery/regeneration apparatus capable of expanding the range of use of the recovered energy, there exists an apparatus equipped with a hydraulic pump motor driven by return hydraulic fluid from a hydraulic actuator, an electric motor that generates power with the drive force of the hydraulic pump motor, and a battery that stores the electric power generated by the electric motor (see, for example, Patent Document 1).